كتاب الأشربة
36  
The Book of Drinks
(18)
Chapter: It is recommended to lick one's fingers and wipe the bowl, and to eat a piece of food that is dropped after removing any dirt on it. It is disliked to wipe one's hand before licking it, because of the possibility that the blessing of the food may be in that remaining part. The Sunnah is to eat with three fingers
(18)
باب اسْتِحْبَابِ لَعْقِ الأَصَابِعِ وَالْقَصْعَةِ وَأَكْلِ اللُّقْمَةِ السَّاقِطَةِ بَعْدَ مَسْحِ مَا يُصِيبُهَا مِنْ أَذًى وَكَرَاهَةِ مَسْحِ الْيَدِ قَبْلَ لَعْقِهَا
Sahih Muslim 2033 c

This hadith has been narrated on the authority of Sufyan with the same chain of transmitters but with a slight variation of wording.

وَحَدَّثَنَاهُ إِسْحَاقُ بْنُ إِبْرَاهِيمَ، أَخْبَرَنَا أَبُو دَاوُدَ الْحَفَرِيُّ، ح وَحَدَّثَنِيهِ مُحَمَّدُ بْنُ، رَافِعٍ حَدَّثَنَا عَبْدُ الرَّزَّاقِ، كِلاَهُمَا عَنْ سُفْيَانَ، بِهَذَا الإِسْنَادِ ‏.‏ مِثْلَهُ ‏.‏ وَفِي حَدِيثِهِمَا ‏ "‏ وَلاَ يَمْسَحْ يَدَهُ بِالْمِنْدِيلِ حَتَّى يَلْعَقَهَا أَوْ يُلْعِقَهَا ‏"‏ ‏.‏ وَمَا بَعْدَهُ ‏.‏
Reference : Sahih Muslim 2033c
In-book reference : Book 36, Hadith 176
USC-MSA web (English) reference : Book 23, Hadith 5045
  (deprecated numbering scheme)